1. Field of the Invention:
The present invention relates to an airbag device for protecting a vehicular occupant by softening a shock of a vehicle collision with an airbag inflated when the vehicle collision takes place.
2. Related Art:
An airbag device is already known as a vehicular occupant protective device to protect a vehicular occupant in case of a vehicle collision. The airbag device comprises a sensor for detecting the vehicle collision, an inflator for erupting gas based on a signal from the sensor, an airbag that inflates with the gas erupted from the inflator, a base plate to which the airbag and the inflator are fixed, etc. At the airbag, a hole portion and a vent hole are formed. The hole portion is used to insert a gas erupting portion of the inflator into the airbag, and the vent hole is used to adjust the pressure caused by gas in the airbag.
FIG. 14 shows an example of an airbag device having such a structure. As shown in FIG. 14, a retaining section of an airbag 2 is sandwiched between a retainer 13 and a base plate 10 and secured by bolts 15 or rivets. A diameter of a hole portion 11 for inserting a gas erupting portion of an inflator 9 into the airbag 2 is designed as large as or larger than a diameter of the gas erupting portion of the inflator 9. Thus the gas erupting portion of the inflator 9 can be inserted into the airbag 2 through the hole portion 11, and the gas from the inflator 9 can be erupted into the airbag 2.
However, in the airbag device shown in FIG. 14, the retaining section of the airbag 2 sandwiched between the retainer 13 and the base plate 10 is extremely small. In case of a vehicle collision, high pressure gas from the inflator 9 to inflate the air bag 2 acts instantaneously inside the airbag 2, and a stress caused by the high pressure gas concentrates on the retaining section which is secured to the base plate 10 with the bolts 15. Therefore, if the airbag 2 is damaged by the stress, there arises a possibility that the retaining section of the airbag 2 slips off the base plate 10.
As another example of prior arts, there is an airbag device disclosed in Japanese Unexamined Patent Publication No. 3-292236. An airbag in the airbag device has at least one slit for inserting an inflator thereinto. The airbag is sandwiched between the inflator and a base plate and secured with bolts.
In the airbag device with the airbag having one slit, there arises a possibility that strength of the airbag decline. That is, if the high pressure gas acts instantaneously inside the airbag, the slit may tear from ends thereof. This causes undesired discharge of the high pressure gas to the outside.